It is the objective of this proposal to study the metabolism of the normal and impaired cardiac conduction system. Although much is known about the unique electrophysiology and histology properties of the Purkinje network, little is understood about its biochemical features. This is explained by the complex anatomy and the paucity of Purkinje cells within the myocardium. Since abnormalities in conduction cause fatal arrhythmias in many patients, a basic understanding of the molecular machinery of the Purkinje cell is an important goal in modern Cardiology. In Phase I, the emphasis will be to elucidate some of the basic pathways of energy metabolism, i.e. of glycogen, glucose, and free fatty acid metabolism and of the phosphate and redox potentials in the cardiac conduction system in normal and ischemic tissue. Quantitative histochemical techniques will be employed to generate three-dimensional metabolic maps of key enzymes, substrates, and cofactors in conduction and contiguous contractile elements. The hormonal and ischemic modulation of these processes and the handling of important ions will then be studied using metabolite, enzyme, cofactor, and second messenger level changes as indicators of molecular mechanisms. In Phase II, single Purkinje cells will be isolated and grown in tissue culture. Electrophysiological studies in single cells will be performed in parallel in normal, ischemic, and pharmacologically altered cells. These studies will be interpreted in light of the metabolic findings. The significance of these experiments lies in attempting for the first time the biochemical characterization of some of the fundamental metabolic processes which govern impulse conduction in cardiac Purkinje cells. For the first time, parallel to metabolic studies electrophysiological and biochemical parameters critical to understanding Purkinje cell function will be studied in normal, diseased, and pharmacologically altered Purkinje cells in culture. This approach promises to provide new insights into both understanding the conduction system at a molecular level and to clinical application of drug therapies in the treatment of cardiovascular disease.